Process for reducing iron in a blast furnace



Nov. 15, 1938. E. 1.. CLAIR PROCESS FOR REDUCING IRON IN A BLAST FURNACEFiled June 10, 2 Sheets-Sheet l Nov, 15, 1938.

L CLAIR PROCESS FOR REDUCING IRON IN A BLAST FURNACE Filed Jun 'io, 19352 Sheets-Sheet 2 Patented Nov. 15, 1938 FUR Edward L. Clair, Toledo,Ohio, assignor to Interlake Iron Corporation, Chicago, 111., acorporation of New York Application June 10, 1935, Serial No. 25,719

5 Claims. (01. 75-41) My invention relates to a metallurgical apparatusand process to be used for the purpose of producing lowcarbon pig iron,and, more particularly, to animproved blast furnace for this 5 purpose.

The procedure followed in producing pig iron is to charge the stack or.furnace to a point Well up in the stack 01 to the stockline. The chargeis made up of iron oxide or ore, solid fuel (usually coke), andlimestone, dolomite, or, other suitable flux. The air blast usuallyenters the furnace through copper water-cooled tuyeres. The air, at apoint very close to the tuyeres, is converted into carbon monoxide (CO)and passes upward, reducing the iron oxideto an impure iron. The hearthand lower part of'the bosh is filled with coke or other solid fuel athigh temperature. As the process proceeds, the impure iron and slag inthe molten form drips down through the column of coke at hightemperature. The finished product, i. e., pig iron, collects in thehearth or crucible of the furnace, from where it is periodically.tapped. The slag floats on the molten iron and is removed from thefurnace at the same time the iron is tapped out and also between taps bydraining it from the slag notch or monkey.

During the descent of the molten iron through the high temperature coke,it absorbs carbon. And during the time intervals between tapping, thefinished product collecting in the hearth is intimately mixed with thehigh temperature coke and continues to absorb carbon.

In the typical blast furnace the portion of the furnace below the tuyerezone, i. e., the hearth or crucible, is of a depth normally at leasttwice the depth of the tuyere zone portion of the furnace. And, in thetypical furnace, this deep bottom or hearth portion contains a singleiron notch for the removal of the iron and one or more suitable openingsat a higher level in the furnace than the iron notch for the removal ofthe slag. It is customary in the typical blast furnace to open thesingle tap hole or iron notch and drain the furnace at regularintervals, commonly every four, five or six hours.

As a resultof the deep hearth'or crucible portion below the center lineof the tuyres and the time intervals between tapping the finishedprodnot from the single iron notch, the production of pig iron in atypicaLblast furnace results in a type of pig iron containingapproximately a total of four percent of carbon. This carbon contentresults in pigs having relatively great carbon segregation, which carbonsegregation a removable bottom detachably secured to the section inorder to facilitate repair and reduce makes the grain structurenon-uniform and reduces the strengthof the iron.

, The object of the present invention is to pro-,- vide an improvedblast furnace and process for the production of iron of carbon contentlower '5 than is possible in a typical blast furnace and withouttreatment of the hot metal aften it leaves the blast furnace.

According to its more specific aspects, the

present invention attains the desired reduction 10 in the amount ofcarbon contained in the iron product-by reducing the duration of contactbetween the molten iron and the high temperature coke or other solidfuel. This reduction in the duration of contact between the molten ironand the high temperature fuel is attained, in turn, by. substantiallyreducing the depth of the hearth or crucible, or eliminating the hearthor crucible entirely, and by eliminating the time intervals betweentapping of the iron to. provide for a prac- 20 .tically continuous flowof the finished'iron prodnot from the furnace. 7

Another object is to construct the improved iron blast furnace so thatthe operation in the desired manner will be practically possible andsuccessful, and, further, to apply to the improved iron blast furnacealtype of construction that will make necessary repairs possible withfacility and in a minimum of time. I

Another object is to provide the furnace with bottom of the tuyere zone.This will permit re: moval of the bottom section and substitution ofanother similar section or relining the removed 35 the delay to aminimum. 7

Further objects and the features and advantages of the present inventionwill be apparent from the following detailed description taken in'connection with the accompanying drawings, in which: v

Figure 1 is a fragmentary vertical sectional view F through -a blastfurnace embodying the present invention;

Figure 2 is a horizontal section taken on the .line 2 2 of Figure 1,with the tuyeres in elevation;

Figure 3 is a fragmentary horizontal section through the bottom of ablast furnace embodying the present invention and showing an alternativearrangement of iron tapping holes and a fore-hearth for receiving themolten iron from the furnace; and I Figure 4 is a fragmentary verticalsection taken on the line 44 of Figure 3, showing a, 55

portion of the blast fm'nace, the fore-hearth, and a ladle for receivingthe molten iron from the fore-hearth.

The blast furnace shown in the drawings comprises the bottom section IIIclosing the bottom of the hearth or crucible of the furnace andconsisting of a steel shell ll lined with a refractory material l2. Inthe particular embodiment of the invention illustrated in the drawingsthe furnace has a bosh M in the form of an inverted frustum of a cone,but this may vary widely. The bosh It extends up generally to the line0-0 at the belly or lower end of the conical stack l5.

The shaft, stack, or inwall l5 has a steel shell l6 provided with arefractory lining H. The upperportion of the stack or'inwall I5 is notshown, for it, in no manner, diifers from the stack or inwall-of atypical blast furnace. The bosh M has a steel shell [8 provided with arefractory lining IS. The overhanging lower portion of the stack I5 issupported upon four supporting posts 28 arranged equi-distantly aroundthe lower portion of the furnace. zone l3 has the proper openings 2| topermit inserting the tuyere coolers 22 and tuyres or tuyere nozzles 23through which the blast of air -under pressure is deliveredinto thefurnace in the usual manner. The center line of the tuyeres 23 isindicated by the line H. The bosh walls may becooled by the typicalarrangement of copper cooling plates 24, as well understood in the art.

The crucible or hearth 26, closed at the bottom by the bottom sectionIII, is of adepth sub stantially less than the depth of the hearths orcrucibles heretofore employed. blast furnace prior to the presentinvention the hearth or crucible below the center line 11-11 of thetuyeres is, as already pointed out, of such fixed depth that the normalresult is a high rate of carbon absorption by the molten iron, whereasin the illustrated embodiment of the present invention the depth of thehearth or crucible 26 below the center line b-b of the tuyeres issubstantially less than prior practice so as to shorten the period ofcontact of the molten iron with the solid fuel in order to control thecarbon content in the molten pig iron produced.

This radical reduction in the depth of the hearth or cruciblesubstantially reduces the duration of contact between the molten ironand the high temperature coke or other solid fuel as the iron drips ordescends down through the column of coke to the hearth or crucible 26.And this substantial reduction in the duration of contact between themolten iron and the coke re,- duces the amount of carbon absorbed by theiron, and thereby produces a lower carbon pig iron than possibleheretofore.

The particular amount of reduction in the depth of the hearth orcrucible may, of course, vary widely within the scope of the presentinvention and may, if desired, depend upon the character of the chargeintroduced into the furnace and the carbon content desired in thefinished iron product.

The bottom section III is provided with two or The tuyere In the,typical the present invention. There are, however, preferably two ormore of these holes, as distinguished from the single iron notch of theprior art. In Figures 1 and 2, the four tapping holes 28 are arrangedequidistantly about the bottom of the furnace.

In operation, the iron is tapped from one iron notch 28 after another insuch manner and at such times as will prevent undue wear or burning ofany single notch 28 and, at the same time, permit of keeping the flow ofiron from the furnace practically continuous. This practicallycontinuous flow of iron from the furnace from one notch after anotherprevents prolonged contact between the molten iron and the hightemperature coke or other fuel which, with the hearth or cruciblereduced in depth or eliminated, further reduces the carbon content ofthe resulting pig iron. The holes 28 may be closed in any suitable ordesired manner, as by means of a mud or clay gun as well understood inthe art, and may be opened one after another in any suitable orpreferred manner, as by drilling or by means of a sledge or bar, or byburning with a jet of oxygen.

With the plurality of ironnotches or tapping holes 28 and thesubstantially continuous flow of iron from the furnace by tapping onehole 28 after another, the usual slag openings at a higher point in thefurnace for the removal of slag may be eliminated. The slag is removedwith the molten iron through the iron openings 28, and may be separatedfrom the iron after removal of the same from the furnace. This removalof the slag from the molten iron may be accomplished in a fore-hearth orafter-hearth by permitting the slag to collect upon the top of themolten iron and draining the same periodically therefrom.

' By draining the finished molten iron practically continuously from thebottom of the furnace, as formed from one tapping hole after another,undue wear or burning such as would result if it were attempted to tapthe molten iron continuously from a single iron notch is prevented.

' bottom of the furnace will be more severe than is commonly the case.The bottom section I0 is therefore made removable and is attached alongthe line a--a by means of angle brackets 32 and bolts 33 to the portionof the furnace immediately above the bottom section. This will permitremoving the bottom section l2 and substituting another similar sectionor relining the removed section in order to facilitate the repair andreduce the delay to a minimum.

In the embodiment of Figures 3 and 4, only three iron tapping holes 28'are shown, and these holes are arranged in close proximity to deliverthe molten iron through spouts 35 into a forehearth 36. The tappingholes 28' open through the bottom section l2 as in the precedingembodiment of the invention, and this bottom section [2 is removablyattached by means of angle brackets 32' and bolts 33 to the immediatelyoverlying portion of the furnace.

The fore-hearth 38 has a steel-shell 31 provided with a refractorylining 38. A layer of insulation 39 is interposed between the shell 31and the lining 38. preferably formed of refractory material, has aplurality ofopenings 42, one beneath each of the spouts 35, sothat asthe molten iron is tapped from the respective holes 28' it will enterthe The removable top 40, which is amasso fore-hearth ii. At itsopposite side, theforehearth 36 has an iron tapping hole 43 fordelivering the molten iron from the fore-hearth through a spout 44 intoa ladle 45 for transferring the iron to a pig molding or castingmachine, or elsewhere, as desired.

For the purpose of heatingithe fore-hearth 3 to maintain the hot metalin liquid condition and against cooling to a thickened or pastycondition, the fore-hearth is provided with a suitable burner, indicatedmore or less diagrammatically at 46. This burner 46 is directeddownwardly through the removable top 40 and upon the hot metal in thefore-hearth 3b. The fuel for the burner 46 may be gas, oil, or powderedcoal, coke or the like. In the illustrated embodiment of the invention,suitable gaseous fuel is delivered under pressure by means of apipe-line connected to the burner 46.v A suitable supply of air may beprovided for the gas supplied to the burner. The fore-hearth 36 isprovided with an opening 50 at a higher level than the iron tapping hole43 for the removal of slag, orthe slag which will float on the hot metalin the forehearth may be removed therefrom in any other suitable orpreferred'manner.

- In the'operation of the embodiment of the intically continuous ,flowof iron and slag from.

the furnace and to prevent prolonged contact with the high temperaturecoke; The tapping holes 28' may be opened and closed one after anotherin the manner set forth in connection with the preceding embodiment ofthe invention, or in any other suitable or preferred manner.

' Upon entering the fore-hearth 36, the iron and slag may remain therefor a sufficient time to permit the slag to collect upon the top of themolten iron, all without increasing the contact of the iron withthe hightemperature coke or other fuel, and without further collection ofcarbon. Then, as already pointed out, the slag may be skimmed or drainedfrom the slag notch SI- and the molten iron tapped out through thetapping hole 43 and into the ladle 45.

The type of construction and the degree of departure from the typicalfurnace. both as to depth of bottom and number of iron notchesmore thanone, may be changed in my invention according to the character of thecharge and the carbon content desired in the finished iron product. IThe particular character of the equipment may be varied to suitthe'desired operation and the analysis of the iron to be produced.

I do not intend to be limited to the precise details shown or described.

I claim:

1. In the smelting of iron bearing ore in a blast furnace having tuyeresfor delivering a blast of air into the furnace, the improvement whichcomprises reducing the descent of the molten iron through the furnacebelow the center line of the tuyres to a distance substantially lessthan existing practice, and tapping the molten iron from the furnace atdifferent locations one after another and in practically a continuousstream so as to shorten the period of contact of the molten iron withthe solid fuel in the furnace in order to control the carbon content inthe molten pig iron produced.

2. In the smelting. of iron bearing ore in a blast furnace havingtuyeres for delivering a blast of air into the furnace, the novel stepwhich comprises tapping the molten iron from the furnace at differentlocations one after another and in practically a continuous stream so asto shorten the period of contact of the molten iron with the solid fuelin the furnace in order to control the content of carbon inv the moltenpig iron produced. J

3. In the smelting of iron bearing ore in a blast furnace having tuyeresfor delivering a blast of air into the furnace, the improvement whichcomprises controlling the depth of descent of the molten iron throughthe furnace below the center line of the tuyeres so as to con-. trol theperiod of contact of the molten iron with the solid fuel in the furnaceand thereby control the carbon content in the molten pig iron produced.

4.In thesmelting'of ironbearing orein a blast furnace having tuyeres fordelivering a blast of air into the: furnace, the improvement whichcomprises controlling the depth of descent of the molten iron throughthe furnace below the center line of the tuyeres so as to control theperiod of contact ofthe molten iron with the solid fuel in the furnaceand thereby connace at. different locations one'after another generallycircumferentially about the furnace and in practically a continuousstream so as to shorten the period of contact of the molten iron withthe solid fuel in the furnace in order to control the content of carbonin the molten pig iron produced.

' EDWARD L. CLAIR.

